optional
Description
optional is a header operator allowing the expression of "add <something> to field <F>", or add nothing". E.g., optional F:x is equivalent to adding the alternation of F:x with the empty grammar.
Usage examples
Just for illustration, consider the following grammar.
| A = | gloss | optional text |
|---|---|---|
| past | ba |
This produces two entries: {gloss:past, text:ba} and {gloss:past}, because optional text:ba can either add ba to text or just add the empty string.
Why would we want to use this?
The above is not the usual use case (it'd be more readable just to add another line to the table rather than use optional); optional is usually used with embed to express the possible absence of a morpheme. For example, consider this grammar:
| Root = | text | gloss |
|---|---|---|
| gan | run | |
| ik | jump | |
| Evid = | text | gloss |
| a | direct | |
| ba | hearsay | |
| tsu | infer | |
| Stem = | embed | optional embed |
| Root | Evid |
In this grammar, optional embed: Evid is a way of expressing that the evidentiality morpheme is optional. (In this simple example, yes, we could have just added another line to the Stem symbol, but in a more complex grammar we might not want to double the number of lines in Stem just for this. When the column is always optional, it's best to express this in a columnar way with optional rather than adding rows.)
Also note that, by the rules of Gramble syntax, we can't express the ability to leave out evidentiality by adding a line to Evid that's empty in every field -- it would just be interpreted as an empty line and ignored. optional lets you get around that.